1. Field of the Invention
This invention relates to a syringe useful with a medicine, and specifically to a medicine syringe having a piston stroke long enough to facilitate its use even when the internal capacity of a syringe barrel is small and allowing only a small amount of a medical solution to remain in the syringe barrel upon completion of an injection of the medical solution by sliding a piston via a plunger rod.
2. Description of the Related Art
A syringe for use with a medicine varies in capacity and shape depending on its application. In particular, prefilled syringes which are finding increasing utility in recent years have been proposed in diverse designs and sizes, because they have been filled with medical solutions upon distribution from pharmaceutical makers and can hence be designed in shapes and capacities suited for the administration of the medical solutions. On the other hand, there has been a move in recent years toward smaller dose sizes. Keeping in step with this move, syringes to be used are also desired to meet this move toward smaller dose sizes. From the production technology, however, there is generally a restriction to a move toward smaller syringes, because the production of such smaller syringes is difficult. It is, therefore, a current practice to meet the move toward smaller dose sizes, for example, by filling a syringe of 3 mL capacity with a medical solution as little as only one third of its full capacity when desired to store 1 mL of the medical solution.
For the purpose of making more accurate a dose to be administered in addition to the economical viewpoint, there is also a long-standing desire to decrease a medical solution that remains in a syringe after the use of the medical solution, and numerous proposals have been made in this respect. For example, U.S. Pat. No. 5,795,337 to Jean Pierre Grimard discloses a piston-like stopper for use in a syringe barrel. In order to minimize a dead space in which a medical solution enters and is held unusable, the piston-like stopper is provided on a distal end of a stopper main body with a distally-directed, conically-shaped projection and is also provided with at least one elongate discontinuity (e.g., a raised rib, recessed grove, or the like) running along the conically-shaped projection. When a piston-like stopper is formed in such an intricate shape, however, the projection may not always be surely inserted at a distal end thereof into a passageway arranged at a distal end of the syringe barrel, and therefore, the occurrence of malfunction is concerned. For use in a syringe of such an extremely small capacity as a total capacity of not greater than 0.5 mL to which the present invention is directed as will be described subsequently herein, a piston itself is of an extremely small size. Such an extremely small piston is accompanied by a problem in that it can be hardly molded or otherwise formed or worked into such an intricate shape as proposed above and, even if good results are obtained with a usual size, the piston of the usual size cannot be applied as it is.